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Journal Articles

Estimation method of prompt neutron decay constant reducing higher order mode effect by linear combination

Katano, Ryota

Nuclear Science and Engineering, 193(4), p.431 - 439, 2019/04

We proposed "linear combination method" to reduce the higher order mode effect on the prompt neutron decay constant measured by the pulsed neutron experiment. When the spatial higher order mode effect is taken into account, the time evolution of the neutron counts after the pulsed neutron injection is given by linear combination of multiple exponential functions. However, the measurement results by the conventional method include the systematic error derived from the higher order mode effect because the conventional method fit the neutron counts with a single exponential function. The proposed method extract the single exponential function of the fundamental mode by linear combination of the neutron counts at multiple detectors, thus the proposed method reduces the higher order mode effect. As the verification, we applied the proposed method to the numerical simulation. The results indicate that the proposed method can reduce the higher order mode effect by linear combination.

JAEA Reports

Annual report of Nuclear Science Research Institute, JFY2013 & 2014

Nuclear Science Research Institute

JAEA-Review 2018-036, 216 Pages, 2019/03


Nuclear Science Research Institute (NSRI) is composed of Planning and Coordination Office, Fukushima Project Team and six departments, namely Department of Operational Safety Administration, Department of Radiation Protection, Engineering Services Department, Department of Research Reactor and Tandem Accelerator, Department of Fukushima Technology Development and Department of Decommissioning and Waste Management, and each departments manage facilities and develop related technologies to achieve the "Middle-term Plan" successfully and effectively. In order to contribute the future research and development and to promote management business, this annual report summarizes information on the activities of NSRI of JFY 2013 and 2014 as well as the activity on research and development carried out by Nuclear Safety Research Center, Advanced Research Center, Nuclear Science and Engineering Center and Quantum Beam Science Center, and activity of Nuclear Human Resource Development Center, using facilities of NSRI.

Journal Articles

Assessment of the potential for criticality in the far field of a used nuclear fuel repository

Atz, M.*; Salazar, A.*; Hirano, Fumio; Fratoni, M.*; Ahn, J.*

Annals of Nuclear Energy, 124, p.28 - 38, 2019/02

 Percentile:100(Nuclear Science & Technology)

The likelihood for criticality in the far field of a repository was evaluated for direct disposal of commercial light water reactor used nuclear fuel. Two models were used in combination for this evaluation: (1) a neutronics model to estimate the minimum critical masses of spherical, water-saturated depositions of fuel material; (2) a transport model to simulate the dissolution of fuel material from multiple canisters and the subsequent transport of the solutes through host rock to a single accumulation location. The results suggest that accumulation of a critical mass is possible under conservative conditions but that these conditions are unlikely to occur, especially in the vicinity of a carefully-arranged repository.

Journal Articles

Study of the screening survey using an ambient dose equivalent rate survey meter in criticality accidentsy

Hoshi, Katsuya; Tsujimura, Norio; Yoshida, Tadayoshi; Kurihara, Osamu*; Kim, E.*; Yajima, Kazuaki*

Progress in Nuclear Science and Technology (Internet), 6, p.152 - 155, 2019/01

Journal Articles

Study on criticality in natural barrier for disposal of fuel debris from Fukushima Daiichi NPS

Shimada, Taro; Takubo, Kazuya*; Takeda, Seiji; Yamaguchi, Tetsuji

Progress in Nuclear Science and Technology (Internet), 5, p.183 - 187, 2018/11

After fuel debris is removed from the reactor containment vessel at Fukushima Daiichi NPS (1F) and collected in waste containers in the future, the waste containers will be disposed at a deep geological repository. The uranium inventory and uranium-235 ($$^{235}$$U) enrichment of the fuel debris are larger than those of high-level vitrified wastes which are produced from liquid waste during reprocessing of spent nuclear fuels. Therefore, there is a possibility not to be excluded that a criticality occurs in the geological media where the uranium precipitates at the far-field from the repository, after the uranium located in the repository is dissolved by groundwater. In this study, we calculated the quantity of uranium precipitated at the natural barrier, and studied dimension of uranium deposited in the natural barrier and carried out the criticality analysis.

Journal Articles

Investigation of uncertainty caused by random arrangement of coated fuel particles in HTTR criticality calculations

Ho, H. Q.; Honda, Yuki; Goto, Minoru; Takada, Shoji

Annals of Nuclear Energy, 112, p.42 - 47, 2018/02

 Times Cited Count:1 Percentile:100(Nuclear Science & Technology)

Journal Articles

A Power spectrum approach to tally convergence in Monte Carlo criticality calculation

Ueki, Taro

Journal of Nuclear Science and Technology, 54(12), p.1310 - 1320, 2017/12


 Times Cited Count:2 Percentile:42.02(Nuclear Science & Technology)

In Monte Carlo criticality calculation, confidence interval estimation is based on the central limit theorem (CLT) for a series of tallies. A fundamental assertion resulting from CLT is the convergence in distribution (CID) of the interpolated standardized time series (ISTS) of tallies. In this work, the spectral analysis of ISTS has been conducted in order to assess the convergence of tallies in terms of CID. Numerical results indicate that the power spectrum of ISTS is equal to the theoretically predicted power spectrum of Brownian motion for effective neutron multiplication factor; on the other hand, the power spectrum of ISTS for local power fluctuates wildly while maintaining the spectral form of fractional Brownian motion. The latter result is the evidence of a case where a series of tallies is away from CID, while the spectral form supports normality assumption on the sample mean.

JAEA Reports

A Guide to introducing burnup credit, preliminary version (English translation)

Okuno, Hiroshi; Suyama, Kenya; Ryufuku, Susumu*

JAEA-Review 2017-010, 93 Pages, 2017/06


There is an ongoing discussion on the application of burnup credit to the criticality safety controls of facilities that treat spent fuels. With regard to such application of burnup credit in Japan, this document summarizes the current technical status of the prediction of the isotopic composition and criticality of spent fuels, as well as safety evaluation concerns and the current status of legal affairs. This report is an English translation of A Guide to Introducing Burnup Credit, Preliminary Version, originally published in Japanese as JAERI-Tech 2001-055 by the Nuclear Fuel Cycle Facility Safety Research Committee.

Journal Articles

On-line subcriticality measurement using a pulsed spallation neutron source

Iwamoto, Hiroki; Nishihara, Kenji; Yagi, Takahiro*; Pyeon, C.-H.*

Journal of Nuclear Science and Technology, 54(4), p.432 - 443, 2017/04

 Times Cited Count:4 Percentile:27.27(Nuclear Science & Technology)

Journal Articles

Monte Carlo criticality analysis under material distribution uncertainty

Ueki, Taro

Journal of Nuclear Science and Technology, 54(3), p.267 - 279, 2017/03

 Times Cited Count:3 Percentile:27.27(Nuclear Science & Technology)

Analysis framework under material distribution uncertainty is investigated for the Monte Carlo (MC) criticality calculation of continuously mixed media formed via molten core concrete interaction. Deterministic trigonometric functions and randomized Weierstrass functions are utilized to represent the spatially continuous variation. Numerical results indicate that the effective multiplication factor (k$$_{rm eff}$$) under random spatial variation can depart significantly from the k$$_{rm eff}$$ of a reference uniform medium. It is also shown that the deterministic modeling provides an upper-bound measure for extreme results from random realizations.

Journal Articles

International Conference on Nuclear Criticality Safety ICNC2015

Nauchi, Yasushi*; Takezawa, Hiroki*; Tonoike, Kotaro

Nippon Genshiryoku Gakkai-Shi, 58(4), p.247 - 252, 2016/04

no abstracts in English

JAEA Reports

Study on release behavior of radioiodine from fuel solution under criticality accident condition

Tashiro, Shinsuke; Abe, Hitoshi

JAEA-Technology 2015-044, 20 Pages, 2016/03


In order to estimate public dose under a criticality accident in fuel solution of a fuel reprocessing plant, release behavior of radioiodine from the fuel solution to atmosphere is very important. In this report, time evolution of $$^{133}$$I concentration in gas phase of TRACY core tank was measured until the concentration in the solution decreased. Furthermore, cumulative release ratio (CRR) and release rate (RR) from the solution to the atmosphere of radioiodine were evaluated by applying previously-reported evaluation model. As a result, for the case of short transient criticality, RR of $$^{133}$$I became maximum at 1 hour later from the ending and almost constant after 8 hour later. Furthermore, relationship of each elapsed time between total fission number and release rate of $$^{133}$$I could be derived. On the other hand, for the case of long criticality excursion, such as JCO criticality accident, the CRR and RR of radioiodine increased monotonously with time.

Journal Articles

Benchmark models for criticalities of FCA-IX assemblies with systematically changed neutron spectra

Fukushima, Masahiro; Kitamura, Yasunori; Kugo, Teruhiko; Okajima, Shigeaki

Journal of Nuclear Science and Technology, 53(3), p.406 - 424, 2016/03

 Times Cited Count:6 Percentile:17.95(Nuclear Science & Technology)

JAEA Reports

Criticality safety evaluation for the direct disposal of used nuclear fuel; preparation of data for burnup credit evaluation (Contract research)

Yamamoto, Kento*; Akie, Hiroshi; Suyama, Kenya; Hosoyamada, Ryuji*

JAEA-Technology 2015-019, 110 Pages, 2015/10


In the direct disposal of used nuclear fuel (UNF), criticality safety evaluation is one of the important issues since UNF contains some amount of fissile material. The recent development of higher-enrichment fuel has enhanced the benefit of the application of Burnup Credit. In the present study, the effects of the several parameters on the reactivity of disposal canister model were evaluated for used PWR fuel. The parameters are relevant to the uncertainties of depletion calculation code, irradiation history, and axial and horizontal burnup distribution, which are known to be important effect in the criticality safety evaluation adopting burnup credit. The latest data or methodology was adopted in this evaluation, based on the various latest studies. The appropriate margin of neutron multiplication factor in the criticality safety evaluation for UNF can be determined by adopting the methodology described in the present study.

Journal Articles

Inter-code comparison of TRIPOLI${textregistered}$ and MVP on the MCNP criticality validation suite

Brun, E.*; Zoia, A.*; Trama, J. C.*; Lahaye, S.*; Nagaya, Yasunobu

Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.351 - 360, 2015/09

This paper presents a joint work conducted at CEA Saclay and JAEA Tokai aimed at comparing the Monte Carlo codes TRIPOLI${textregistered}$ and MVP on a selection of ICSBEP benchmarks. Our goal is to establish a common set of Monte Carlo input decks, as a basis for rigorous inter-code comparison in criticality-safety. As a reference, we will use the MCNP Criticality Validation Suite: other Monte Carlo developers might easily join that effort in the future. For the purpose of inter-code comparison, the TRIPOLI${textregistered}$ and MVP input decks have been translated from those of MCNP, without any further assumptions. Both TRIPOLI${textregistered}$ and MVP have been run with the same ENDF/B-VII.0 evaluated nuclear data, and as far as possible the same simulation options as in the original LANL work. In this abstract, we present preliminary results on the BIGTEN benchmark. In the full paper these will be extended to the 31 benchmarks of the MCNP Criticality Validation Suite. In the future, this database will also help in the analysis of sensitivity to nuclear data, CPU times and figures of merit.

Journal Articles

Nuclear criticality safety standard for a fuel reprocessing plant assuming burnup credit published by the Atomic Energy Society of Japan

Nakajima, Ken*; Itahara, Kuniyuki*; Okuno, Hiroshi

Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.496 - 502, 2015/09

An outline of the standard "Procedures for Applying Burnup Credit to Criticality Safety Control of a Reprocessing Facility: 2014" (AESJ-SC-F025: 2014) published in April 2015 by the Atomic Energy Society of Japan (AESJ) is presented. The AESJ published more than 60 Standards. However, many of them were in the field of nuclear power reactors or radioactive wastes. Ten years ago the AESJ published "Basic Items of Criticality Safety Control: 2004" (AESJ-SC-F004:2004), which prescribed basic ideas, requirements and methods on nuclear criticality safety controls of facilities handling with nuclear fuel materials in general for preventing a nuclear criticality accident. However, it did not include any specific procedures for adopting burnup credit. Therefore, a new standard was envisaged as the first Standard for fuel reprocessing plants, which clarified the specific procedures to apply burnup credit to designers, operators, maintenance persons and administrators.

Journal Articles

Study on criticality control of fuel debris by Japan Atomic Energy Agency to support Nuclear Regulation Authority of Japan

Tonoike, Kotaro; Yamane, Yuichi; Umeda, Miki; Izawa, Kazuhiko; Sono, Hiroki

Proceedings of International Conference on Nuclear Criticality Safety (ICNC 2015) (DVD-ROM), p.20 - 27, 2015/09

From the viewpoint of safety regulation, criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Station would be a risk-informed control to mitigate consequences of criticality events, instead of a deterministic control to prevent such events. The Nuclear Regulation Authority of Japan has set up a research and development program to tackle this challenge. The Nuclear Safety Research Center of Japan Atomic Energy Agency, commissioned by the authority, has launched activities such as computations of criticality characteristics of the fuel debris, development of criticality risk assessment method, and preparation of criticality experiments to support them.

Journal Articles

Journal Articles

Assessment of human body surface and internal dose estimations in criticality accidents based on experimental and computational simulations

Sono, Hiroki; Ono, Akio*; Kojima, Takuji; Takahashi, Fumiaki; Yamane, Yoshihiro*

Journal of Nuclear Science and Technology, 43(3), p.276 - 284, 2006/03

 Times Cited Count:1 Percentile:88.21(Nuclear Science & Technology)

For a study on the applicability of a personal dosimetry method to criticality accident dosimetry, an assessment of the human body surface and internal dose estimations was performed by experimental and computational simulations. The experimental simulation was carried out in a criticality accident situation at the TRACY facility. The neutron and $$gamma$$-ray absorbed doses in muscle tissue were separately estimated by a dosimeter set of an alanine dosimeter and a thermoluminescence dosimeter made of enriched lithium tetra borate with a phantom. The computational simulation was conducted with a Monte Carlo code taking account of dose components of neutrons, prompt $$gamma$$-rays and delayed $$gamma$$-rays. The computational simulation was ascertained to be valid by comparison between the calculated dose distributions in the phantom and the measured ones. The assessment based on the experimental and computational simulations confirmed that the personal dosimetry using the dosimeter set provided a first estimation of the body surface and internal doses with precision.

Journal Articles

Extension of effective cross section calculation method for neutron transport calculations in particle-dispersed media

Yamamoto, Toshihiro; Miyoshi, Yoshinori; Takeda, Toshikazu*

Journal of Nuclear Science and Technology, 43(1), p.77 - 87, 2006/01

 Times Cited Count:5 Percentile:57.94(Nuclear Science & Technology)

no abstracts in English

208 (Records 1-20 displayed on this page)